Systems and methods for percutaneous access and formation of arteriovenous fistulas

ABSTRACT

A catheter system includes a proximal base having a distal diagonal end surface and a distal tip connected to the proximal base and movable relative to the proximal base, wherein the distal tip has a proximal diagonal end surface. The distal diagonal end surface and the proximal diagonal end surface contact opposing sides of a tissue portion to create the fistula. A peripheral edge defines the proximal distal end surface. A proximal point is disposed on the peripheral edge. The proximal point comprises a shortened angle and a fully radiused edge relative to a remaining portion of the peripheral edge and a relief recess is disposed on a distal end of the proximal base, both for the purpose of minimizing tissue snagging.

This application claims the benefit under 35 U.S.C. 119(e) of the filingdate of Provisional U.S. Application Ser. No. 62/208,353, entitledProtected Distal Tip Systems and Methods, filed on Aug. 21, 2015, whichapplication is expressly incorporated herein by reference, in itsentirety.

BACKGROUND OF THE INVENTION

In the body, various fluids are transported through conduits throughoutthe organism to perform various essential functions. Blood vessels,arteries, veins, and capillaries carry blood throughout the body,carrying nutrients and waste products to different organs and tissuesfor processing. Bile ducts carry bile from the liver to the duodenum.Ureters carry urine from the kidneys to the bladder. The intestinescarry nutrients and waste products from the mouth to the anus.

In medical practice, there is often a need to connect conduits to oneanother or to a replacement conduit to treat disease or dysfunction ofthe existing conduits. The connection created between conduits is calledan anastomosis.

In blood vessels, anastomoses are made between veins and arteries,arteries and arteries, or veins and veins. The purpose of theseconnections is to create either a high flow connection, or fistula,between an artery and a vein, or to carry blood around an obstruction ina replacement conduit, or bypass. The conduit for a bypass is a vein,artery, or prosthetic graft.

An anastomosis is created during surgery by bringing two vessels or aconduit into direct contact. The vessels are joined together with sutureor clips. The anastomosis can be end-to-end, end-to-side, orside-to-side. In blood vessels, the anastomosis is elliptical in shapeand is most commonly sewn by hand with a continuous suture. Othermethods for anastomosis creation have been used including carbon dioxidelaser approaches and a number of methods using various connectedprostheses, clips, and stents.

An arterio-venous fistula (AVF) is created by connecting an artery to avein, and to create a leak-free blood flow path between them. This typeof connection is used for hemodialysis, to increase exercise tolerance,to keep an artery or vein open, or to provide reliable access forchemotherapy.

An alternative is to connect a prosthetic graft from an artery to a veinfor the same purpose of creating a high flow connection between arteryand vein. This is called an arterio-venous graft, and requires twoanastomoses. One is between artery and graft, and the second is betweengraft and vein.

A bypass is similar to an arteriovenous graft. To bypass an obstruction,two anastomoses and a conduit are required. A proximal anastomosis iscreated from a blood vessel to a conduit. The conduit extends around theobstruction, and a second distal anastomosis is created between theconduit and vessel beyond the obstruction.

As noted above, in current medical practice, it is desirable to connectarteries to veins to create a fistula for the purpose of hemodialysis.The process of hemodialysis requires the removal of blood from the bodyat a rapid rate, passing the blood through a dialysis machine, andreturning the blood to the body. The access to the blood circulation isachieved with 1) catheters placed in large veins, 2) prosthetic graftsattached to an artery and a vein, or 3) a fistula where an artery isattached directly to the vein.

Hemodialysis is required by patients with kidney failure. A fistulausing native blood vessels is one way to create high blood flow. Thefistula provides a high flow of blood that can be withdrawn from thebody into a dialysis machine to remove waste products and then returnedto the body. The blood is withdrawn through a large access needle nearthe artery and returned to the fistula through a second large returnneedle. These fistulas are typically created in the forearm, upper arm,less frequently in the thigh, and in rare cases, elsewhere in the body.It is important that the fistula be able to achieve a flow rate of 500ml per minute or greater in order for the vein to mature or grow. Thevein is considered mature once it reaches >4 mm and can be accessed witha large needle. The segment of vein in which the fistula is createdneeds to be long enough (>6 cm) to allow adequate separation of theaccess and return needle to prevent recirculation of dialyzed andnon-dialyzed blood between the needles inserted in the fistula.

Fistulas are created in anesthetized patients by carefully dissecting anartery and vein from their surrounding tissue, and sewing the vesselstogether with fine suture or clips. The connection thus created is ananastomosis. It is highly desirable to be able to make the anastomosisquickly, reliably, with less dissection, and with less pain. It isimportant that the anastomosis is the correct size, is smooth, and thatthe artery and vein are not twisted.

SUMMARY OF THE INVENTION

The present invention eliminates the above described open procedures,reduces operating time, and allows for consistent and repeatable fistulacreation.

The present invention comprises a device for creating a percutaneousarteriovenous (AV) fistula, which comprises a proximal base having adistal diagonal end surface and a distal tip connected to the proximalbase and movable relative to the proximal base. The distal tip has aproximal diagonal end surface. A first heating assembly, comprising anembedded energized heating element, is disposed on at least one of thedistal diagonal end surface and the proximal diagonal end surface. Asecond heating assembly, comprising a passive non-energized heatspreader, is disposed on the other distal diagonal end surface. Thedistal diagonal end surface and the proximal diagonal end surface areadapted to contact opposing sides of a tissue portion to create thefistula. The distal diagonal end surface is oriented at an angle of15-90 degrees relative to a longitudinal axis of the device, and moreadvantageously at an angle of 15-50 degrees relative to the longitudinalaxis. In one particularly optimal configuration, the distal diagonal endsurface is oriented at an angle of approximately 23 degrees relative tothe longitudinal axis. The angle of the proximal diagonal end surfacematches the angle of the distal diagonal end surface, so that the twosurfaces match one another while working on opposite sides of thetissue.

A shaft is provided for connecting the distal tip to the proximal base,the shaft being extendable and retractable to extend and retract thedistal tip relative to the proximal base. A resilient member in thedistal tip manages pressure in the weld.

The proximal diagonal end surface has an embedded heating elementdisposed thereon. An energized heating element optimally comprises aserpentine configuration within a thermally conductive material. Atemperature sensor is disposed near the energized heating element withinthe conductive material, for providing closed loop temperature controlto the heater.

The heat spreader on the proximal face of the distal tip comprises athermally conductive material which extends across a substantial portionof the diagonal end surface on which it is disposed, the heat spreaderbeing in thermal contact with the energized heating element to conductheat from the heating element and spread the heat across the diagonalend surface. It is constructed so that it has a thickness approximatelyequal to a thickness of a vessel in which the device is deployed, thisthickness falling within a range of 0.010 inches to 0.060 inches. Thisis done for optimum radial conduction of heat into tissues. Otherconfigurations optimize heat spreader thickness for insertion. In thisapplication, a smaller profile is desired.

In one configuration, the heat spreader comprises a raised segmentforming a rib, for creating a focused heat conduction path throughtissue which will quickly cut or ablate tissue. This creates the openingin the fistula through which the blood will flow. After creating theopening, raised segment contacts the heat spreader on the opposingdiagonal surface to heat said spreader up to a welding temperature. Thetissue between the spreaders are then held at temperatures and pressuresrequired to fuse the tissues together.

The distal tip comprises a distal diagonal outer surface containing anaperture for a through lumen for receiving a guidewire. The distaldiagonal surface and the diagonal heat spreader surface are connectedwith a resilient media which maintains the appropriate pressure fortissue welding.

A position sensor is provided for monitoring movement of the distal tipwith respect to the proximal base. This relative position indicates thethickness of tissue captured prior to fistula creation. This informationcan be valuable in determining if the procedure is proceeding properly.Vessel wall thicknesses are seen on ultrasound and can be estimated.This vessel wall thickness should be reflected in the position sensor.When cutting through tissue, the position sensor should indicate whenthe tissues are penetrated.

In another aspect of the invention, there is provided a method forcreating an arteriovenous (AV) fistula, which comprises steps ofselecting an appropriate procedural site having each of a primary vesseland a secondary vessel in close proximity to one another, inserting apiercing device into the primary vessel to pierce the vessel walls, andcreating an opening so that the piercing device extends into theadjacent secondary vessel, and advancing a guidewire until the guidewireis positioned in a blood flow path of the secondary vessel sufficientlyto allow the piercing device to be removed. The piercing device is thenwithdrawn. A proximal end of the guidewire is loaded into the distallumen of a device for dilating the guidewire's path through bothvessels. The proximal end of the dilator is then loaded into the lumenof a sheath and advanced through both vessels. The dilator is thenremoved and replaced by the device. The distal tip of the device is thenadvanced to place the proximal and distal diagonals in the first andsecond vessels. The sheath is then removed so that the proximal anddistal diagonal jaw faces directly oppose the first and second vesselwalls.

At this juncture, a heater on the diagonal distal surface of theproximal base is seated against an inner wall of the first vesselsurrounding the opening. The distal tip is retracted so that the heatspreader on the diagonal proximal surface of the distal tip seatsagainst an inner wall of the second vessel surrounding the opening,thereby capturing the walls of the first and second vessel between thefacing angled surfaces of each of the distal tip and the proximal base,respectively.

The distal tip and the proximal base are pulled together, and at thesame time energy is applied to the heating element on the distaldiagonal surface of the proximal base. The resultant applied heat andmotion causes the raised rib on the heater to cut or ablate throughtissue until the raised rib contacts the heat spreader on the distaltip. The raised rib allows tissue to reside between the embedded heaterand the heat spreader. The proximal heater transfers heat to the distalheat spreader by direct conduction from the contact of the raised ribwith the distal heat spreader The distal heat spreader floats on aresilient base contained within the tip while in contact with theproximal heater. Sufficient energy is applied to weld tissue. The deviceis then removed leaving a welded fistula with blood flow sufficient tosupport dialysis.

In still another aspect of the invention, a method of creating a passagebetween adjacent primary and secondary vessels is disclosed, comprisinga step of positioning a sheath across both vessels at the fistula site,introducing the device into the sheath so that its distal mechanisms areplaced appropriately in relation to the vessel walls, removing thesheath, actuating a cutting mechanism in the device to open acommunicating aperture from the primary to secondary vessel, andactuating a welding mechanism in the device to weld both vesselstogether.

In yet another aspect of the invention, there is provided a cathetersystem for creating an arteriovenous (AV) fistula, which comprises aproximal base having a distal diagonal end surface and a distal tipconnected to the proximal base and movable relative to the proximalbase, wherein the distal tip has a proximal diagonal end surface Thedistal diagonal end surface and the proximal diagonal end surface areeach adapted to contact opposing sides of a tissue portion to create thefistula. A peripheral edge defines the proximal distal end surface. Aproximal point is disposed on the peripheral edge. Advantageously, theproximal point comprises a shortened angle and a fully radiused edgerelative to a remaining portion of the peripheral edge.

Another advantageous feature of the present invention is the provisionof a relief recess disposed on a distal end of the proximal base. Thecatheter system is disposed along an operating axis and the reliefrecess is peripherally spaced from the proximal point on an opposed sideof the axis relative to the proximal point. When a sheath is disposedabout the proximal base, the sheath having a distal end wherein aportion of the sheath distal end is disposed on the relief recess, aspace is created at another peripheral portion of the sheath distal endinto which the proximal point may pass, thereby minimizing the chancethat the proximal point will snag adjacent tissue.

Yet another advantageous feature of the invention is the provision of astop formed in a peripheral edge of the distal diagonal end surface ofthe proximal base, the stop being disposed at a peripheral locationdirectly aligned with the proximal point, so that the stop will engagethe proximal point to prevent tissue snagging.

A shaft is provided for connecting the distal tip to the proximal base,the shaft being extendable and retractable to extend and retract saiddistal tip relative to the proximal base. Additionally, a heatingassembly comprising an energizable heating element is disposed on atleast one of the distal diagonal end surface and the proximal diagonalend surface.

In still another aspect of the invention, there is provided a cathetersystem for creating an arteriovenous (AV) fistula, which comprises aproximal base having a distal diagonal end surface and a distal tipconnected to the proximal base and movable relative to the proximalbase. The distal tip has a proximal diagonal end surface. The distaldiagonal end surface and the proximal diagonal end surface are adaptedto contact opposing sides of a tissue portion to create the fistula.Advantageously, a relief recess is disposed on a distal end of theproximal base.

The catheter system may further comprise a peripheral edge defining theproximal distal end surface and a proximal point on the peripheral edge.The catheter system is disposed along an operating axis and the reliefrecess is peripherally spaced from the proximal point on an opposed sideof the axis relative to the proximal point. A sheath is disposed aboutthe proximal base, the sheath having a distal end wherein a portion ofthe sheath distal end is disposed on the relief recess, wherein a spaceis created at another peripheral portion of the sheath distal end intowhich the proximal point may pass.

A stop may be formed in a peripheral edge of the distal diagonal endsurface of the proximal base, the stop being disposed at a peripherallocation directly aligned with the proximal point. A shaft forconnecting the distal tip to the proximal base is provided, the shaftbeing extendable and retractable to extend and retract the distal tiprelative to the proximal base. A heating assembly comprising anenergizable heating element may be disposed on at least one of thedistal diagonal end surface and the proximal diagonal end surface.

The invention, together with additional features and advantages thereof,may best be understood by reference to the following description takenin conjunction with the accompanying illustrative drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is an elevational view of the handle portion of a deviceconstructed in accordance with one embodiment of the present invention;

FIG. 1b is an elevational enlarged view of the circled distal workingportion of the device of FIG. 1 a;

FIG. 2a is an elevational view of an embodiment like that shown in FIGS.1a-1b , with the distal end in a first working configuration;

FIG. 2b is an elevational view similar to FIG. 2a , with the distal endin a second working configuration;

FIG. 3 is an isometric view of one embodiment of the device shown inFIGS. 1a -2 b;

FIG. 4a is an exploded isometric view illustrating an embodiment of theproximal base and particularly showing the assembly of the embeddedheater;

FIG. 4b is an isometric view showing the embedded heater;

FIG. 5 is an exploded isometric view of the distal tip showing the heatspreader, the resilient member, and the guidewire lumen;

FIG. 6 is an isometric view of the distal tip;

FIG. 7a is a diagram depicting the insertion of the guidewire intovessels;

FIG. 7b is a diagram depicting the insertion of the dilator intovessels;

FIG. 7c is a diagram depicting the insertion of the sheath into vessels;

FIG. 8 is a diagram depicting the insertion of the device into thesheath;

FIG. 9 is a diagram depicting the retraction of the sheath and placementof the device within vessels;

FIG. 10 is a diagram depicting the placement of the device with respectto vessels during welding and cutting;

FIG. 11 is a diagram showing the flow through vessels as a result of thedevice's service;

FIG. 12 is a diagram of an anastomosis creating using the devices andmethods disclosed in the present application;

FIG. 13 shows a flow diagram of a medical procedure, using an AV fistulacreating device according to at least certain embodiments;

FIG. 14 is a view of a catheter which may be used in connection with theforegoing embodiments for compressing tissue;

FIG. 15 is a plan view of a catheter like that shown in FIG. 14,illustrating a problem that can occur because of high pressures on thecatheter during use;

FIG. 16 is an isometric view of the catheter shown in FIGS. 14-15,illustrating one feature that can contribute to or reduce the issue ofshifting of the distal tip due to high applied pressures;

FIG. 17 illustrates a catheter like those shown in FIGS. 14-16 whereinthe distal tip has been shifted to counter expected changes in thecatheter because of applied pressure during use;

FIG. 18 illustrates a catheter like those shown in FIGS. 14-17 whereinanother change has been introduced to reduce issues related to shiftingof the distal tip during use;

FIG. 19 illustrates a relief feature included on a catheter like thoseshown in FIGS. 14-18 for improving functionality of the catheter duringuse;

FIG. 20 shows a catheter similar to that shown in FIG. 19, wherein afurther feature has been incorporated into the design to improvefunctionality; and

FIG. 21 illustrates a catheter like those shown in FIGS. 19 and 20disposed within an introducer sheath.

DETAILED DESCRIPTION OF THE INVENTION Notation and Nomenclature

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies that design and manufacture medical devices mayrefer to a component by different names. This document does not intendto distinguish between components that differ in name but not function.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection, or through anindirect connection via other devices, components, and connections.Further, the terms “proximal” and distal are intended to refer toproximity relative to a bone anchor applicator. Thus, if a first deviceis distal and a second device is proximal, the second device is nearerto the bone anchor applicator than the first device.

Reference to a singular item includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “an,” “said” and “the”include plural references unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement serves as antecedent basis foruse of such exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Lastly, it is to be appreciated that unless definedotherwise, all technical and scientific terms used herein have the samemeaning as commonly understood by one of ordinary skill in the art towhich this invention belongs.

Where a range of values is provided, it is understood that everyintervening value, between the upper and lower limit of that range andany other stated or intervening value in that stated range isencompassed within the invention. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein.

All existing subject matter mentioned herein (e.g., publications,patents, patent application and hardware) is incorporated by referenceherein in its entirety except insofar as the subject matter may conflictwith that of the present invention (in which case what is present hereinshall prevail). The referenced items are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such material by virtue of prior invention.

Before the various embodiments are described in detail, it is to beunderstood that this invention is not limited to particular variationsset forth herein as various changes or modifications may be made, andequivalents may be substituted, without departing from the spirit andscope of the invention. As will be apparent to those of skill in the artupon reading this disclosure, each of the individual embodimentsdescribed and illustrated herein has discrete components and featureswhich may be readily separated from or combined with the features of anyof the other several embodiments without departing from the scope orspirit of the present invention. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,process, process act(s) or step(s) to the objective(s), spirit or scopeof the present invention. All such modifications are intended to bewithin the scope of the claims made herein. The technology disclosedherein would have a broad application in vessel surgery for an animal,such as a human. This includes surgery of ducts, ureters, arteries,veins, grafts, or any other tubular structure that transports material.Some of these procedures include, but are not limited to, artery tovenous fistula creation, vascular repair, coronary artery bypass graftsurgery, femoral popliteal bypass, transjugular intrahepaticportosystemic shunt, splenorenal shunt, or a mesocaval shunt.

Referring now more particularly to the drawings, as illustrated in FIGS.1a and 1b , one embodiment of the inventive intraluminal anastomoticdevice 1 comprises a catheter 1 a, including a proximal heating assembly2, a proximal shaft 3, a distal heating assembly 4, and a handpiece 6.The distal heating assembly 4 comprises a distal tip 5 and heat spreader24. The handpiece 6 comprises a tip actuation button 7 and a releasebutton 13. The proximal heating assembly 2 is constructed of a proximalbase 10 that is cut at an angle θ at the distal end.

On the diagonal surface 10 a of the proximal base 10, a heating element8 is embedded. The proximal base 10 is typically constructed of athermally insulating material that is resistive to high temperatures. Anembedded heater 12 is used to compress and heat the tissue to createcoaptation of vessel tissues. This process is known as tissue welding ortissue fusion. In one embodiment, the embedded heater 12 is constructedof a thermally conductive material with the resistive heating elementembedded therein.

FIG. 4a and FIG. 4b show the construction of embedded heater or heatingsurface 12. Heating element 8 takes on a serpentine configuration toincrease length and, therefore, surface area leading to higher energydensities. Heating element 8 is attached inside of a mating cavity fromwhich power attachment leads 11 extend and are inserted into lumens 11 awhere they are attached to conductors that extend back to handpiece 6.Ribs 9 are a part of embedded heater 12 and are also made of aconductive material. Ribs 9 will heat up to initially cut tissue priorto welding. Ribs 9 move into rib relief 15 on heat spreader 24 to cuttissue (see FIG. 5).

The proximal base 10 is configured with at least one thermocouple ortemperature sensor 14 shown in FIG. 1b to monitor the temperature nearthe active heating element 8, and provides a means for closed looptemperature control to optimize tissue welding and cutting. The proximalbase is designed to reside in primary vessel 20 (FIG. 9) duringdeployment.

As illustrated in FIGS. 1-3, the distal tip 5 terminates in a diagonalsurface at angle θ. A guidewire lumen 18 extends through the center ofthe distal tip 5, as shown in FIG. 3. Distal heating assembly 4 isdesigned to reside in secondary vessel 22 (FIG. 9) during deployment.Distal tip 5 moves with center shaft 16 to desired distance d as shownin FIGS. 2a and 2b . Movement is generally to bring distal tip 5 towardthe proximal heating assembly 2, thereby capturing vessel wall tissuesbetween the two components 2 and 4 for the purpose of welding saidtissues together. A proximal end surface 5 a of the distal heatingassembly 4 is angled to precisely match the angle θ of the proximalheating assembly 2. This is designed so that components 2 and 4 capturevessel tissue between parallel surfaces.

The proximal base 10 is configured as shown in FIGS. 4a and 4b . Theproximal base 10 is configured to receive heating element 8 (FIGS. 4aand 4b ), which is covered by heating surface 12. The heating surface 12is comprised of a thermally conductive material which draws heat fromheating element 8. Power attachment points 11 ensure that heatingelement 8 may be energized. The heating surface 12 transfers heat intothe adjoining vessels to create a weld and/or cut tissue to create ananastomosis or fistula 25 (FIG. 12). The size and shape of heatingsurface 12 mirrors the anastomosis to be created. The thickness of theheating surface 12 is approximately the thickness of the vessel in whichthe weld is being created. However, the thickness may be increased ordecreased to control the amount of heat that is conducted into thesurrounding tissue. Typical thickness of the heating surface ranges from0.010 inches to 0.060 inches (FIGS. 3a-3b, 4a-4c ).

The embodiment illustrated in FIGS. 2a and 2b provides distal tipfeedback, wherein movement of the distal heating assembly 4, from d₂ tod₁, is converted to a signal by a position sensor 36 within thehandpiece 6, or alternatively, outside of handpiece 6. This movement canthen be displayed and/or utilized for a control algorithm. A signal thatrelays the absolute position of the distal heating assembly 4 from theposition sensor 36 to a display device (not shown) of some type, throughan output signal cable 34 is valuable for verifying the tip positionthroughout the procedure and for determining the thickness of the tissuebetween the tip and base of the catheter 1 a before, during, and afterthe formation of the fistula 25 (FIG. 12). The tissue thickness isrelated to the distance measurement by the equation T=d sin θ. Thetissue thickness before the procedure can be correlated to the length ofthe fistula post-procedure. The relative position of the distal heatingassembly 4 during the formation of the fistula 25 is also valuable andcan be related to the rate of tissue dessication, cutting and welding.This signal may be used as an input to control heat application. Forexample, in FIG. 2a , the proximal heating assembly 2 and distal heatingassembly 4 are spaced by a distance d₁, prior to the procedure.

Based upon the type and thickness of the tissue through which theanastomosis is being created, and other factors related to functionalityand durability of the fistula, tip position after the procedure canprovide confirmation that the tissue was properly desiccated and bothvessel walls have been cut. The position of the tip can be verifiedusing the sensor(s) 36.

Referring now particularly to FIGS. 7a through 10, a method for usingthe device 1 will be described. To begin the inventive method ofintravascular access and communication, the practitioner selects anappropriate procedural site having each of a primary vessel 20 and asecondary vessel 22 in close proximity to one another. In currentlypreferred approaches, the primary vessel 20 comprises a vein, and thesecondary vessel 22 comprises an artery, but the invention is notlimited to this arrangement. Initially, a piercing device is insertedinto the primary vessel 20 and actuated to pierce the vessel walls andextend into the adjacent secondary vessel 22. Once penetration fromprimary vessel 20 to secondary vessel 22 has been achieved, guidewire 17is advanced until positioned in the blood flow path of blood vessel 22sufficiently to allow the piercing device to be removed while retainingthe guidewire's position in blood vessel 22.

Once guidewire 17 is sufficiently in position as shown in FIG. 7a , thepractitioner withdraws the piercing device completely from the body,thus leaving the guidewire in the desired position and crossing fromprimary vessel 20 to secondary vessel 22 as shown in FIG. 7a and asdescribed in block 40 of the flow chart illustrated in FIG. 13. Oneexemplary piercing system and methods is disclosed in co-pending U.S.application Ser. No. 13/668,190, commonly assigned with the presentapplication, and expressly incorporated herein by reference, in itsentirety, but any suitable piercing system and method may be used withinthe scope of the present invention.

Guidewire 17 now provides a track over which the rest of the procedureis performed. First and second vessel openings 28 and 29, respectivelymust be dilated so that a sheath 19 (FIG. 7b ) and device 1 may haveaccess. FIG. 7b shows a dilator 27 advancing over guidewire 17 to dilatevessel 20 at opening 28 and vessel 22 at opening 29 in anticipation ofneeding these openings to advance sheath 19 and finally device 1.

Creating openings 28 and 29 in the blood vessels 20 and 22 is a stepthat is carefully engineered. The tortuosities involved in device accessacross openings 28 and 29 mandate that both of the dilator 27 and thesheath 19 be made of flexible materials. These tortuosities are furthercomplicated by the need for tapers on the dilator 27 and sheath 19 to belong. Openings 28 and 29 in vessels need to be created in such a waythat there are no tears.

Tears in openings 28 and 29 will immediately start to bleed. Blood thatenters the fistula site will affect the patency of the tissue weld.Blood needs to stay out of the extra-vessel welding site. Tears createdat this point will have minutes to bleed into the extra-vessel spaceuntil the procedure advances to tissue welding. Tears can also causeopenings 28 and 29 to not seal sufficiently by device 1.

To make openings 28 and 29 without tears, tapers need to be long,smooth, lubricious and, importantly, un-interrupted.

Devices with tapered tips may also heat up part of their tip in thetissue welding. This, with the combined aggravation of interrupting theblood flow, does cause blood to coagulate within the vessel. The shorterthe tip, the less coagulating affects the device during the procedure.It is because of this dynamic that device 1 is shown to have a blunttip, although variable lengths and tapers can be used to accommodatevariable vessel size. As can be seen in FIG. 10, the blunt profile isless intrusive to blood flow.

The inventive method of fistula creation continues with the advancementof sheath 19 as shown in FIG. 7c and as described in block 42 of FIG.13. Sheath 19 is preferably a design with a very thin wall thatcontinuously tapers to a cross-sectional dimension of nearly nothing atits distal tip. It is also very lubricious. Terumo's 6F Radial ArterySheath “Glide Sheath Slender” is an exemplary example. Such a sheathcan, in concert with an appropriate dilator, dilate a vessel wall whileimparting minimal stress to the dilated tissues. This is important inthat it minimizes tearing and also maximizes tissue recovery.

Room is then created for device 1 inside of sheath 19 by the removal ofdilator 27 and as described in block 42 of FIG. 13. Guidewire 17 may ormay not be removed at this point as well. This is a safety issue left upto the practitioner. Device 1 is then inserted into the patient byloading into the proximal end of sheath 19 and optionally over guidewire17. The device 1 is advanced further into the patient until center shaft16 is centered at the anastomosis site as in FIG. 8 and as described inblock 44 of FIG. 13.

Ultrasound and/or fluoroscopy is used at this point to determine wheretube 16 is relative to vessels 20 and 22. Ultrasound doesn't have theresolution and depth to indicate where the vessel walls are in relationto the embedded heater 12 face and heat spreader 24 faces. Manipulationof the device without a sheath can unknowingly move vessels around andactually get them intertwined and folded around device 1, especiallyaround tube 16 and the proximal edge of heat spreader 24. These dynamicsare hard to track under ultrasound and may go unnoticed. Proceeding withthe cutting and welding on such unorganized tissue does not produce aviable fistula.

Because sheath 19 and dilator 27 do not disrupt vessels 20 and 22, thisalignment is easier to approximate while device 1 is inside sheath 19.Alignment with the sheath in place avoids moving vessels around withdevice 1, as it is isolated from the vessels by the sheath. Adjustmentsto the relative placement of device 1 with vessels 20 and 22 do not movevessels 20 and 22 and are, therefore, not stressed. Less movement of thevessels, especially at openings 28 and 29, mean less stress imparted onthe vessel openings. This minimizes tearing and maximizes elasticrecovery and promotes improved coaptation for welding and cutting. Themethod of fistula creation continues by retracting sheath 19 and asdescribed in block 46 of FIG. 13. Because sheath 19 has a verylubricious un-interrupted tapering outer surface, it can be removedwithout disturbing the alignment of center shaft 16 to the fistula site.Vessel openings 28 and 29 have not been overly stressed and elasticallyrecover to seal around center shaft 16. A slight tension is applied tothe embedded heater 12 to seat it against the vessel wall and promotevessel apposition. The blunt shape of the heat spreader 24 on the distaltip 5 prevents the distal tip from inadvertently retracting back throughthe vessel wall. The heat spreader 24 of the distal heating assembly 4is then retracted to close the spacing between until the walls of thefirst and second vessels 20 and 22, respectively, are captured betweenthe facing blunt surfaces of embedded heater 12 and distal heat spreader24.

The method of fistula formation continues, as described in block 48 ofFIG. 13, by applying a controlled tension between distal tip 5 andproximal base 10, and at this juncture, with the vessels securelyclamped, energy is applied to proximal heating element 8. As embeddedheater 12 heats up, rib 9 cuts through the vessel walls and embeddedheater 12 will contact heat spreader 24. When fully retracted, thesystem is designed so that the two heating elements come into directcontact with one another to ensure a complete cut and capture of thevessel tissue.

Fistula formation continues, as described in block 48 of FIG. 13. Aftervessel walls are cut, rib 9 now contacts heat spreader 24 to conductheat into the spreader for the purposes of welding the vessels together.Rib 9 floats inside of the rib relief 15 on heat spreader 24. Heatspreader 24 is spring loaded by both resilient member 26 (FIG. 1b ) andspring tension on center shaft 16 to ensure proper pressures aremaintained for tissue welding. Two springs are desirable because of theuncertain forces transmitted through tube 16. Tube 16 has high normalfrictional forces imposed by angle θ which can be influenced by thevariable coefficient of friction between tube 16 and proximal shaft 2.This coefficient of friction will change based on fluids within thefistula, tolerances within device 1, and the progress of coagulation ofblood within the interface. This friction can vary by as much as afactor of 8. Resilient member 26 acts directly on the tissue interfacewith no frictional interference. This enables better assurance that theproper pressures are imparted on the tissues while welding.

Regarding the tissue welding process, more particularly, the DCresistive energy functions to fuse or weld the vessels together,creating an elongate aperture 25 (FIG. 12) through the opposing walls ofeach of the first and second vessels, as well as any intervening tissue.As formed, the elongate aperture may typically resemble a slit. However,as pressurized flow begins to occur through aperture 25, which creates acommunicating aperture between the first and second blood vessels, theaperture widens in response to the pressure, taking the shape of anellipse as it opens to form the desired fistula. The effect isillustrated in FIG. 12. The edges 21 of the aperture are cauterized andwelded. Outwardly of the weld band 21 is a coaptation area 23. As shown,the cut area corresponds to the shape of the heating or cutting element.It can be of multiple shapes, such as round, oval, a slit, or acombination as shown. The area adjacent to the cut has been approximatedand welded due to the flat face of the catheter 1 a in the vein (firstvessel) being larger than the embedded heater 12. The heat from theembedded heater 12 is also preferably spread over this area by aconductive material that can be above, below or within the embeddedheater 12 or base 10.

Now that fistula 25 has been fully formed, as described in block 50 ofFIG. 13, the entire instrument 1 and, optionally, guidewire 17 arewithdrawn. Fluid flow is now established between vessels 20 and 22through fistula 25 as shown in FIG. 11.

In another modified embodiment, embedded heater 12 and heating element 8may be merged into the same component. The welding and cutting surfacescan be smaller so as to approximate the dimensions of the heatingelement, making this change practical. The dimensions of heating element8 will determine the resistance across power attachment points 11. Thisresistance in relation to the resistance of the leads conducting energyto heater element 8 is critical. As the resistance across points 11lowers and approximates the resistance in the leads, the leads willstart to burn a good portion of the power, heating up proximal shaft 6and requiring more energy to be delivered to accomplish the same weld.Heating element is made longer by its serpentine shape, thus increasingits resistance to minimize this effect. Choosing a heating elementmaterial with greater resistance will also help. In another modifiedembodiment, rib relief 15 may be eliminated, and ribs 9 formed tocontact a surface on heat spreader 24. The nature of this contact andthe shapes of the surfaces may enhance thermal cutting with mechanicalcutting. The mechanical cutting may be accomplished by putting sharpedges on the ribs that interact with heat spreader 24 so as to sheartissue. Heat spreader 24 may also have surfaces or edges that work inconcert with features on ribs 9 to mechanically cut tissue. Thesecutting designs maximize the final contact area between ribs 9 and theheat spread so that sufficient heat transfer is available to thespreader to weld tissues together in the next step.

Welding is possible without resilient member 26 and rib relief 15.Tissue will be trapped in a gap controlled by the height of rib 9. Thecompliance of tissue within that gap will dictate the pressure underwhich it is welded. In some designs and applications, this issufficient.

The distal tip 5 can have a uniform conical tapered outer surface,though it can have a variable tapered, sloped outer surface, wherein theouter surface tapers down to the approximate diameter of a guidewire toprovide an atraumatic method for passing through the vessel wall. Thisis especially desirable if sheath 19 is inadvertently removed beforedistal tip 5 is placed in second vessel 22 and may be viewed as a safetyfeature. The choice to use this embodiment may be influenced bypractitioner skills and experience, anatomy, or patient health.

Device 1 does not require guidewire 17 for placement within sheath 19 assheath 19 provides secure placement. Consequently, device 1 need notcontain provisions for advancement over the guidewire such as lumen 18.Lumen 18 might still exist and serve as a conduit for the transport ofmaterials used in the creation of the fistula such as drugs, biologicfluids, or an adhesive.

+ Energy settings may change to weld tissues at other temperatures.Energy may be modulated based upon the impedance of the tissue ortemperature feedback. Different energy application durations, or cyclicpulses may be used to maximize welding while minimizing heat transfer toadjacent tissues. The distal tip 5 is configured to have insulatingproperties to minimize heat transfer to adjacent tissues and/or fluids.As noted above, the entire surface of the proximal and distal heatelements is configured to have a non-stick coating, such as PTFE, tolimit tissue adhesion.

It is advantageous for the proximal and distal heating assemblies 2 and4 to have a non-stick surface to prevent denatured tissue from bondingto the device. If tissue bonds to the device, the weld between vesselscan be damaged or weakened during removal of the device. Multipledifferent coatings or surface modifications can be applied to thecomponents to create a non-stick surface.

In the embodiment of FIG. 3, it is advantageous that a center shaft 16also have a non-stick surface to prevent coagulated blood and tissuefrom bonding to the surface and obstructing the annular gap between theoutside diameter of the center shaft 16 and the inside diameter of theproximal heating assembly 2. If blood or tissue bonds to or obstructsthis annular gap, this may prevent effective compressive forcetransmission to the distal heating assembly 4 and compromise tissue weldfusion or tissue cutting.

The compression force of the distal heating assembly 4 influences theweld quality of the tissue. If too much pressure is applied, distalheating assembly 4 may quickly cut through the tissue. A balance of heatand pressure is required to dessicate and denature the protein in thetissue to promote adhesion. In order to best achieve this, resilientmember 26 is placed behind heat spreader 24. Resilient member 26 may bepre-compressed in its placement between heat spreader 24 and distal tip5. This will enable resilient member 26 to best approximate a linearforce thus ensuring the proper pressure is applied to tissue duringwelding. Resilient member 26 is preferably made out of silicone. Commoncompression springs could also be used coiled or Belleville springs madeout of bio-compatible materials.

In one embodiment, the lumen 18 is sized to receive a 0.014 inchguidewire, but may be sized to receive guidewires of various diameters.Larger and smaller guidewires are sometimes preferred. Larger diameterguidewires offer more support to transport devices and resistprolapsing. Smaller guidewires are less likely inadvertently penetratetissues and can navigate tortuosities easier. Such dynamics are known tothose familiar with the art.

In one embodiment, the proximal base 10 is cut at an angle θ of 23degrees, forming a distal diagonal end surface 10 a. However, the angleθ can be adjusted depending on the particular anatomy of a proceduralsite and desired anastomosis length. The inventors have found that theangle θ provides advantageous outcomes within a range of about 15-90degrees, and more particularly within a range of 15-50 degrees, keepingin mind that approximately 23 degrees is presently a particularlypreferred angle within that range. These preferred angles/angle rangesresult in an optimized oval configuration for the anastomosis whichmaximizes the cutting surface while also efficiently utilizing availableheating energy to create an effective cut and welding zone.

A variety of DC resistive energy profiles may be used to achieve thedesired cutting. For example, a rapidly stepped or ramped increase toachieve and maintain a desired temperature setting of 150° C.-600° C.may be applied to cut through the vessel walls.

Regarding materials, in one preferred embodiment, the outside diameterof the center shaft 16 and inside diameter of the proximal heatingassembly 2 have a surface finish of <16 Ra, have an annular gap of0.0005-0.0002 inches, and are coated using a high temperature Parylene.Other non-stick coatings, such as Poly Tetra Fluoro Ethylene (PTFE),Titanium Nitride (TiN), Chromium Nitride (CrN), Dicronite, silicone, orother similar coatings known to those skilled in the art may be used toprevent tissue adherence.

Materials known to work well for proximal base 10 and shaft 4 includeVespel, Celazol, Teflon, Polyimide, Ultem, and ceramics.

Examples of thermally conductive material suitable for the constructionof embedded heater 12, and ribs 9, and heat spreader 24 includealuminum, stainless steel, aluminum nitride, or other metal or ceramicmaterials known to those skilled in the art.

Now, with reference to FIGS. 14-21, a catheter 1 a usable in theintraluminal anastomotic device 1 shown and described in FIGS. 1-13 isillustrated. As noted above, a function of the catheter 1 a is tocompress tissue within a tissue space 51 disposed between the distal tip5 and the proximal base 10, and particularly between the proximalsurface 5 a of the distal tip 5 and the distal surface 10 a of theproximal base 10. The center shaft 16 connects the distal tip 5 to theproximal base 10, and is typically fixedly attached at its distal end tothe distal tip 5, and slidably attached at its proximal end to theproximal base 10, so that the shaft 16 can slide within a center lumen52 in the proximal base 10 (see FIG. 4a ), in order to permit the distaltip to move axially relative to the proximal base. Having the baseattached fixedly, and the tip slidably connected is also possible.

The angled catheters of the type shown in the system described in thisapplication absorb significant pressures during use. This pressure isapplied as a part of such steps as cutting, welding, or otherwisemechanically manipulating or clamping the tissue. The basic constructionof the catheter 1 a can make it unstable at the pressures itexperiences, thereby sometimes causing the distal tip 5 of the catheterto mismatch with the proximal base 10 in the direction of arrow 54 (FIG.15). As the distal tip 5 exerts pressure on the proximal base 10, thedistal tip 5 tends to slide on its angled surface 5 a, relative to theproximal base angled surface 10 a. Only the stiffness of the shaft 16opposes this tendency to slide. But, the pressures can be such that theshaft 16 either bends or distorts its foundation in the proximal base10, thereby allowing the distal tip 5 to slide down along its angledsurface, as shown by the arrow 54. As this sliding continues, a proximalpoint 56 along a peripheral edge 55 of the distal diagonal surface 10 amismatches with its mating base and becomes a barb 56 (FIG. 15) that maysnag on tissue or other catheter instruments, thereby impairing functionand/or catching on tissue so that removal of the instrument becomes moredifficult.

Tension on the center shaft 16 magnifies the side load by the inverse ofthe sine of angle θ, shown also in FIG. 15. This is three times thetension in the shaft when the angle θ is about 20 degrees. Thisphenomenon powers the distortion that causes the barb 56.

The center shaft 16 in this design is the stabilizing member in thestructure, that keeps the angled faces 5 a and 10 a aligned. Keeping atolerance or gap 58 (FIG. 16) close between the shaft and the lumen 52is one way to keep the distal tip 5 from side-shifting due to the taper.However, a relatively loose tolerance 58 is shown, because a tighttolerance causes other difficulties in manufacturing and operation. Insome uses of the catheter 1 a, the angled surfaces 5 a and 10 a, asdescribed above, are heated. If the materials used in the constructionof the catheter are subject to softening by this heat, they may deformwhen subject to high sideloads caused by applied pressure. This heating,therefore, tends to magnify the problem of the creation of the barb 56.

In many circumstances, catheter 1 a may be used in controllablecircumstances. The amount of tension on the center shaft 16 may alwaysbe similar, the type of tissue clamped within the tissue space 51 mayalways be the same, the thickness of the tissue may always be the same,and the environmental temperature may always be the same. If thecatheter 1 a is intended for use in these kinds of predictableenvironments, the distance through which the distal tip 5 slides alongthe angled surfaces 5 a, 10 a is likely to be predictable. Thispredictability enables the catheter 1 a to function without snaggingtissue if it is pre-disposed in the opposite direction. This concept isillustrated in FIG. 17, wherein the catheter 1 a is constructed with theproximal point 56 shifted to be offset in a direction opposite to arrow54 by a distance equal to the anticipated distance to be traversedduring the sliding process noted above. Thus, when the catheter 1 a isfully loaded, the barb 56 will only slide to a position even with edge60 on distal surface 10 a, thereby reducing or eliminating the tendencyto snag tissue.

Tensions in the center shaft 16 can easily overcome the same shaft'sability to resist a side load, especially if the angle θ is less than 35degrees. This will happen even if the tolerances 58 on the center shaftand its bearing hole 52 are very tight. Other mechanical features mustbe brought into play to enable the rest of the system to functionproperly.

There are many interactions that such a catheter 1 a may have with othercomponents, and many ways in which this offset barb 56 can be moderatedto a point of functionality. The simplest way is to shorten the lengthof the barb 56 and to put a full radius 62 on it. Unfortunately, thisapproach also decreases the catheter's operating footprint with thetissue which may also decrease its functionality.

FIG. 19 shows a modified embodiment of the catheter 1 a whicheffectively shifts an original operating axis 64 of the catheter 1 aupwardly to new axis 66. This axial shift is in the direction of thebarb 56. A relief recess 68 facilitates this shift by allowing thecatheter to move down its operating aperture. This enables the barb 56to be free of intimate contact with the top of the catheter's operatingaperture, thus preventing the barb 56 from interacting with and snaringtissue or other catheter-related system components, such as a sheath.

In other catheter designs, it may be possible to insert a stop 70 on theangled base so that the barb 56 hits the stop when higher tensionalforces cause the catheter tip to mismatch. Such a stop requiresshortening the distal tip angle 72 in a manner similar to that shown inFIG. 18.

FIG. 21 shows the catheter 1 a inside of a sheath 19. Introducer sheathsare commonly used in connection with a dilator and guidewire to gainaccess to blood vessels. The distal tip of the sheath is very thin andfits tightly with the outside of the catheter 1 a. This is a situationwhere barb 56 will catch a distal end 74 of the sheath 19 very easily.Because the relief 68 is incorporated into the catheter 1 a, space 76 isgenerated due to the gentle shifting of the sheath distal end 74 withinthe relief 68. Space 76 allows the barb 56 to pass into the sheathdistal end 74, as shown in FIG. 21, thereby eliminating theaforementioned snagging risk. In this embodiment, the barb 56 isradiused, as shown in FIGS. 18 and 20.

Accordingly, although an exemplary embodiment and method according tothe invention have been shown and described, it is to be understood thatall the terms used herein are descriptive rather than limiting, and thatmany changes, modifications, and substitutions may be made by one havingordinary skill in the art without departing from the spirit and scope ofthe invention.

What is claimed is:
 1. A catheter system for creating an arteriovenous(AV) fistula, comprising: a proximal base having a distal diagonal endsurface; a distal tip connected to the proximal base and movablerelative to the proximal base, the distal tip having a proximal diagonalend surface, the distal diagonal end surface and the proximal diagonalend surface being adapted to contact opposing sides of a tissue portionto create the fistula; a peripheral edge defining said proximal distalend surface; and a proximal point on said peripheral edge, wherein saidproximal point comprises a shortened angle and a fully radiused edgerelative to a remaining portion of said peripheral edge.
 2. The cathetersystem as recited in claim 1, and further comprising a relief recessdisposed on a distal end of the proximal base.
 3. The catheter system asrecited in claim 2, wherein the catheter system is disposed along anoperating axis and the relief recess is peripherally spaced from theproximal point on an opposed side of the axis relative to the proximalpoint.
 4. The catheter system as recited in claim 1, and furthercomprising a sheath disposed about said proximal base, the sheath havinga distal end wherein a portion of the sheath distal end is disposed onsaid relief recess, wherein a space is created at another peripheralportion of the sheath distal end into which the proximal point may pass.5. The catheter system as recited in claim 1, and further comprising astop formed in a peripheral edge of the distal diagonal end surface ofthe proximal base, the stop being disposed at a peripheral locationdirectly aligned with the proximal point.
 6. The system as recited inclaim 1, and further comprising a shaft for connecting the distal tip tothe proximal base, the shaft being extendable and retractable to extendand retract said distal tip relative to the proximal base.
 7. The systemas recited in claim 1, and further comprising a heating assemblycomprising an energizable heating element disposed on at least one ofthe distal diagonal end surface and the proximal diagonal end surface.8. A catheter system for creating an arteriovenous (AV) fistula,comprising: a proximal base having a distal diagonal end surface; adistal tip connected to the proximal base and movable relative to theproximal base, the distal tip having a proximal diagonal end surface,the distal diagonal end surface and the proximal diagonal end surfacebeing adapted to contact opposing sides of a tissue portion to createthe fistula; and a relief recess disposed on a distal end of theproximal base.
 9. The catheter system as recited in claim 8, and furthercomprising: a peripheral edge defining said proximal distal end surface;and a proximal point on said peripheral edge.
 10. The catheter system asrecited in claim 9, wherein the catheter system is disposed along anoperating axis and the relief recess is peripherally spaced from theproximal point on an opposed side of the axis relative to the proximalpoint.
 11. The catheter system as recited in claim 10, and furthercomprising a sheath disposed about said proximal base, the sheath havinga distal end wherein a portion of the sheath distal end is disposed onsaid relief recess, wherein a space is created at another peripheralportion of the sheath distal end into which the proximal point may pass.12. The catheter system as recited in claim 10, and further comprising astop formed in a peripheral edge of the distal diagonal end surface ofthe proximal base, the stop being disposed at a peripheral locationdirectly aligned with the proximal point.
 13. The system as recited inclaim 8, and further comprising a shaft for connecting the distal tip tothe proximal base, the shaft being extendable and retractable to extendand retract said distal tip relative to the proximal base.
 14. Thesystem as recited in claim 8, and further comprising a heating assemblycomprising an energizable heating element disposed on at least one ofthe distal diagonal end surface and the proximal diagonal end surface.